A look at flu transmission and vaccine efficacy with Jonathan Sugimoto

As the past year’s events surrounding the novel H1N1 pandemic proved, simply having a good vaccine for a highly infectious disease is not sufficient if that vaccine is in short supply. It’s important to know how the disease is transmitted, who is most infectious and who is in the most danger from the disease in order to decide how to allocate the vaccine.

One way to get at how flu is transmitted is to study isolated outbreaks of the disease. University of Washington Epidemiology graduate student Jonathan Sugimoto, working with the research group of VIDI members Dr. Ira Longini and Dr. Betz Halloran, studied an outbreak of novel H1N1 influenza in a school camp near Olympia, Wash. in April 2009. Nearly 100 children from four different schools attended the camp, and Public Health – Seattle King County and the U.S. Centers for Disease Control and Prevention gathered data on how many kids in the camp got sick, and then how many of their family members came down with the flu after the children returned home. Sugimoto and his colleagues then used that data to look at the transmission of clinical H1N1 in the camp and in households.

The camp study and other corroborating studies found high rates of secondary transmission among groups of children, such as in schools and camps, but as compared to seasonal flu and previous flu pandemics, Sugimoto and colleagues found lower than expected rates of transmission of H1N1 flu in households. 51 percent of children in the camp got sick, but a much lower percentage of the sick children’s family members came down with the flu after being exposed. Part of this is due to the age effect, Sugimoto said, where children appear to be more susceptible to flu in general. But that doesn’t fully explain the low transmission rates they see in households.

“With a virus that’s obviously able to transmit around the world, we’re a little surprised to be seeing such low household secondary attack rates compared to what we’d expect given the demonstrated transmissibility of the virus,” Sugimoto said.

One possibility is that analyses of flu transmission may underestimate the number of household members that are already immune to novel H1N1, Sugimoto said.

Sugimoto is also working with PATH, the French Institute of Research for Development, and the Ministry of Health in Senegal on the transmissibility of seasonal flu and efficacy of the seasonal flu vaccine. PATH is running a community trial of the injectible seasonal flu vaccine in 10,000 Senegalese children, and Sugimoto has built a survey into the structure of that trial to look at how infectious people contact other people within their compounds and villages and the resulting transmission of the seasonal flu, and whether the vaccine changes those transmission rates.

“There are various components to influenza vaccine efficacy,” Sugimoto said. “Nobody has really estimated the efficacy of the vaccine to reduce your ability to transmit to someone else. So we’re going to try to estimate that for the first time.”

Sugimoto hopes his work on seasonal and H1N1 flu will provide input for policymakers on vaccination decisions. “If people know where the transmission is occurring in the community, we will know where to target interventions, if we can,” he said.